1. Field of the Invention
The present invention relates to a communication apparatus capable of detecting for example the state of a communication line and effecting communication according to the result of said detection.
2. Related Background Art
In such technical field, there is already known, for example, a facsimile apparatus which is connected to a telephone line and which includes a line (network) control unit, a reader unit for reading an image, a recorder unit for recording an image, a modem unit for modulation/demodulation of signals, etc.
Also there is popularly used an automatic answering telephone apparatus (or message phone apparatus) which is likewise connected to a telephone line and is provided with an outgoing message (OGM) transmitting unit for effecting automatic call reception in the absence of a receiver and sending an outgoing message for requesting the message recording to a caller, and an incoming message (ICM) recording/reproducing unit for recording an incoming message from the caller in response to said OGM and reproducing said ICM afterwards.
Such automatic answering telephone apparatus is generally so designed as to be capable of recording and reproducing ordinary speech done by a user through the communication line when he is present at home, by means of the ICM recording/reproducing unit.
Also in recent years, there has been commercialized facsimile apparatus with automatic answering telephone function (or message phone function), in which a facsimile mechanism, an auto answering mechanism, a speech communication mechanism and a line control unit for connecting these mechanisms with the line are integrally constructed.
FIG. 3 illustrates such apparatus in a block diagram, wherein a line control unit NC and a speech communication unit CC (primary circuits) are separated by transformers from a message recorder unit RC and a facsimile machine FC (secondary circuits). Thus, in case of speech communication recording in which the speech by the speech communication unit CC is recorded, the speech by said unit CC is transmitted through a transformer to the message recorder unit RC and recorded therein.
In such apparatus, however, the speech through the speech communication unit is recorded, and a transformer is required merely for recording the speech. Also, such speech recording is not possible if the speech communication unit is not equipped together.
Also there is known a facsimile apparatus in which an answering telephone automatically responds to an incoming call, and then the communication is switched to facsimile if a caller is a facsimile apparatus.
The network control unit of such apparatus is constructed as shown in FIG. 4, wherein terminals L1, L2 are connected to a telephone line, and terminals T1, T2 are connected to an automatic answering telephone (message phone). There is provided a CML (connect line to modem) relay which connects the telephone line to the answering telephone or to the modem for facsimile communication.
Said CML relay 301 is connected to the message phone (contacts a) in the stand-by state.
A call signal Ci, arriving from the telephone line in said stand-by state, enters the message phone through a current sensor 320. Upon detecting said Ci signal, the message phone effects automatic response (or occupies the line), whereby a DC current of several ten milliampere flows in the current sensor 320, consisting for example of a photocoupler composed of an LED (light-emitting diode) and a phototransistor. If a caller is a facsimile apparatus, a call tone signal-CNG is superposed with said DC current. Said CNG signal is supplied, through a DC intercepting capacitor 303, a transformer 304 and an amplifier 305, to a terminal ACDET.
A control unit of the facsimile apparatus, upon detection of a DC current from a terminal DCDET indicating the response by the message phone, detects the frequency of the signal released from the ACDET terminal, and switches the CML relay to the modem for facsimile communication if the detected signal is identified as the CNG signal of 1100 Hz.
In the above-explained apparatus, however, the transformer 304 has been the obstacle to compactization.
Since the CNG signal current is overlaid on the DC current, it has been proposed to detect both currents by the current sensor 320, but the detection of the CNG signal is sometimes difficult depending on the resistance of the line or the impedance of the telephone, since the photocoupler composed of LED and phototransistor shows considerable fluctuation in the current transmission rate and has a narrow range for realizing linear transmission of the CNG signal.
In the field of facsimile apparatus with automatic answering (or message recording) function, the present applicant already made proposals in the U.S. Pat. No. 4,800,439 and the U.S. patent application Ser. No. 49,948 filed May 15, 1987, but such proposals are not to resolve the above-explained drawbacks.